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Additive manufacturing, or 3D printing, is a process where a part is produced layer by layer, and represents a promising approach for designing components close to their final shape. Titanium alloys produced by additive manufacturing find application in various industries. This overview examines the features of the formation of the microstructure and properties in Ti alloys synthesized with the use of powder and wire laser additive technologies, as well as solid-phase methods of additive manufacturing such as friction stir additive manufacturing. Their main drawbacks and advantages are discussed, as applied to Ti alloys. The main approaches to solving the problem of increasing the strength properties of the synthesized Ti workpieces are considered. The authors of this overview propose a new area of research in the field of the application of additive technologies for producing ultrafine-grained Ti semi-products and parts with enhanced performance characteristics. Research in this area opens up prospects for designing heavily loaded complex-profile products for the aerospace, oil and gas, and biomedical industries. [ABSTRACT FROM AUTHOR]

The last two decades have witnessed significant progress in the development of severe plastic deformation techniques to produce ultrafine-grained materials with new and superior properties. This review examines works and achievements related to the low-temperature superplasticity of ultrafine-grained aluminum alloys. The examples are provided of the possibility to observe low-temperature superplasticity in aluminum alloys at temperatures less than 0.5 Tmelt and even at room temperature, and herein, we demonstrate the cases of achieving high ductility and high strength in aluminum alloys from processing utilizing severe plastic deformation. Special emphasis is placed on recent studies of the formation of segregations of alloying elements at grain boundaries in UFG Al alloys and their influence on the development of grain boundary sliding and manifestation of low-temperature superplasticity. In addition, the current status and innovative potential of low-temperature superplasticity in aluminum alloys are observed. [ABSTRACT FROM AUTHOR]

This study explores the influence of zirconium (Zr) additions on the phase composition, microstructure, and mechanical properties of Ti-2.5Al–5V–5Mo alloy sheets. Through isothermal and polythermal section analysis, we quantified the phase transformations in the Ti–Al–Mo–V–Zr system under varying cooling rates. The introduction of Zr resulted in a refined duplex microstructure, significantly reducing grain size and enhancing mechanical properties. In the temperature range of 600–750 °C, the α/β-phase ratio shifted from 70/30 to 30/70, reflecting optimized phase stability. Post-rolling thermal treatments further refined the microstructure to an ultrafine grain size, which improved yield strength and tensile strength while preserving ductility. The findings demonstrate that precise control over Zr content and thermal processing parameters can achieve an ideal balance between strength and ductility, making these alloys highly suitable for advanced structural applications. This research underscores the potential of Zr-alloyed titanium alloys for industrial use, particularly where enhanced mechanical performance and microstructural stability are critical.

The effect the deformation nanostructuring of copper, nickel, and titanium on ion-induced morphology and sputtering upon high-fluence irradiation with 30-keV argon ions normal to the surface has been studied. The sputtering of a layer commensurate with the size of metal grains induces a homogeneous cone-shaped relief whose stationary erosion proceeds with considerable redepositing of atoms. [ABSTRACT FROM AUTHOR]

The effect of deformation nanostructuring on the ion-beam erosion of copper at a high fluence of irradiation with 30 keV argon ions is experimentally studied. To form an ultrafine-grained structure with a grain size of ~0.4 μm in copper samples with an initial grain size of about 2 μm, deformation nanostructuring by high-pressure torsion is used. It is found that when a layer with a thickness comparable to the grain size is sputtered, a steady-state cone-shaped relief is formed on the copper surface, the appearance of which does not change with increasing irradiation fluence. It is shown that the smaller the grain size in copper, the greater the concentration and the smaller the height of the cones on the surface. The cone inclination angles, close to 82°, as well as the sputtering yield of 9.6 at/ion, are practically independent of the grain size of copper, the thickness of the sputtered layer, and the irradiation fluence. Calculations using the SRIM program show that, when taking into account the redeposition of atoms from the walls of the cones, the sputtering yield of a cone-shaped copper relief Yc is 3.5 times less than the sputtering yield of a single cone, 1.2 times greater than the sputtering yield of a smooth surface, and the value of 9.25 at/ion is close to the experimentally measured one. [ABSTRACT FROM AUTHOR]

A method for pressure welding of cylindrical workpieces in the solid state of an aluminum–zinc alloy in a vacuum at a temperature of 250°C under conditions of low-temperature superplasticity is developed. Tensile tests showed that the strength of the welding joints is 90–95% of the ultimate tensile strength of the base material. [ABSTRACT FROM AUTHOR]

In this work, the technique of equal-channel angular pressing (ECAP) that enables producing bulk billets was used to form a UFG structure in Ti-6Al-4V alloy. A subsequent warm upsetting simulates die forging and the production of a part. We studied the evolution of the UFG alloy's crystallographic texture in the process of deformation during the production of a semi-product and/or a part, as well as its effect on the ductile–brittle transition region in the temperature range from −196 °C to 500 °C and the material's fracture mechanisms. To test Charpy impact strength, standard samples of square cross-section with a V-shape notch were used (KCV). It was found that the impact toughness anisotropy is caused by textural effects and has a pronounced character at temperatures in the ductile–brittle transition range. Up to 100 °C the KCV values are close in the specimens processed by ECAP and ECAP+upsetting (along and perpendicularly to the upsetting axis—along the Z-axis and along the Y-axis, respectively), while a large difference is observed at test temperatures of 200 °C and higher. At a temperature of 500 °C, the impact toughness of the UFG Ti-6Al-4V alloy after ECAP reaches a level of that after ECAP+upsetting in the fracture direction along the Z-axis (1.60 and 1.77 MJ/m2, respectively). Additionally, an additional ECAP upsetting after ECAP decreases the ductile–brittle transition temperature of the UFG Ti-6Al-4V alloy, which increases the temperature margin of the toughness of the structural material and reduces the risk of the catastrophic failure of a product. The fractographic analysis of the fracture surface of the specimens after Charpy tests in a wide temperature range revealed the features of crack propagation depending on the type of the alloy's microstructure and texture in the fracture direction. [ABSTRACT FROM AUTHOR]

The results of the study of the effect of deformation nanostructuring on the formation of a cone-shaped relief on the surface of ultrafine-grained tungsten with an average grain size of 300 nm under high-fluence irradiation with argon ions with an energy of 30 keV are presented. The thermal stability of the resulting cone-shaped relief on the surface and the ultrafine-grained structure in the volume of tungsten under heating up to 1400°C has been studied. Changes in microhardness have been measured. [ABSTRACT FROM AUTHOR]

Additive manufacturing, or 3D printing, is a process where a part is produced layer by layer, and represents a promising approach for designing components close to their final shape. Titanium alloys produced by additive manufacturing find application in various industries. This overview examines the features of the formation of the microstructure and properties in Ti alloys synthesized with the use of powder and wire laser additive technologies, as well as solid-phase methods of additive manufacturing such as friction stir additive manufacturing. Their main drawbacks and advantages are discussed, as applied to Ti alloys. The main approaches to solving the problem of increasing the strength properties of the synthesized Ti workpieces are considered. The authors of this overview propose a new area of research in the field of the application of additive technologies for producing ultrafine-grained Ti semi-products and parts with enhanced performance characteristics. Research in this area opens up prospects for designing heavily loaded complex-profile products for the aerospace, oil and gas, and biomedical industries.

The last two decades have witnessed significant progress in the development of severe plastic deformation techniques to produce ultrafine-grained materials with new and superior properties. This review examines works and achievements related to the low-temperature superplasticity of ultrafine-grained aluminum alloys. The examples are provided of the possibility to observe low-temperature superplasticity in aluminum alloys at temperatures less than 0.5 Tmelt and even at room temperature, and herein, we demonstrate the cases of achieving high ductility and high strength in aluminum alloys from processing utilizing severe plastic deformation. Special emphasis is placed on recent studies of the formation of segregations of alloying elements at grain boundaries in UFG Al alloys and their influence on the development of grain boundary sliding and manifestation of low-temperature superplasticity. In addition, the current status and innovative potential of low-temperature superplasticity in aluminum alloys are observed.

In this study, the microstructural behavior of the advanced Ti-5.7Al-3.8Mo-1.2Zr-1.3Sn-0.15Si (VT8M-1) alloy during rotary swaging (RS) was investigated. VT8M-1 has increased heat resistance and is considered a replacement for the Ti-6Al-4V alloy. It was shown that, during RS, the evolution of the primary a phase is characterized by the formation of predominantly low-angle boundaries according to the mechanism of continuous dynamic recrystallization. The density of low-angle boundaries increases three times: from 0.38 µm−1 to 1.21 µm−1 after RS. The process of spheroidization of the lamellar (a + b) component is incomplete. The average size of globular a and b particles was 0.3 μm (TEM). It is shown that the microstructures after RS (ε = 1.56) and equal-channel angular pressing (ECAP) (ε = 1.4) are significantly different. The temperature–velocity regime and the predominance of shear deformations during ECAP contributed to a noticeable refinement of the primary a-phase and a more complete development of globularization of the lamellar (a+b) component. EBSD studies have shown that RS leads to the formation of a structure with a higher density of low- and high-angle boundaries compared to the structure after ECAP. The results are useful for predicting alloy microstructure in the production of long rods that are further used in forging operations. [ABSTRACT FROM AUTHOR]

Modern materials often have multicomponent alloys, whose properties are determined by their phase and structural composition formed as a result of previous thermomechanical processing. Therefore, the problem of managing the structural state occupies an important place in the overall strategy of developing new materials. Particular attention is drawn to phase transformations in ultrafine systems, in particular, in alloys subjected to severe plastic deformation. In this case, the sample size becomes an important parameter determining the physical properties of the substance and, in particular, its structural and phase compositions. Despite the considerable interest of researchers, until recently, it was not possible to achieve significant theoretical results in this area. Therefore, the development of modern models for describing structural transformations in heterogeneous systems and their application to ultrafine-grained materials seem promising and relevant. [ABSTRACT FROM AUTHOR]

Titanium alloys are widely used in various industries. The most common and well-known titanium alloy is titanium alloy with aluminum and vanadium (Ti-6Al-4V). This alloy is used, for example, in the manufacture of aircraft engines. As part of the development of technologies and the emergence of the evolving requirements for materials, Ti-6Al-4V alloys with ultrafine grains less than 1 μm may become promising. This modification of the alloy has excellent strength characteristics, such as increased fatigue resistance. However, manufacturers are aware of the machinability problem of titanium alloys. To date, a sufficiently high level of understanding of this problem has already been achieved. But, there is practically no information about the machinability of ultrafine-grained alloys and their comparison, in this regard, with the usual coarse-grained version. This study presents the results of experimental studies on the influence of cutting parameters (cutting speed, V, m/min; feed rate, Fz, mm/rev) on the roughness and microstructure of the surface of Ti-6Al-4V samples with coarse-grained and ultrafine-grained structures produced via equal-channel angular pressing. It is shown that turning at a low cutting speed (V = 48 m/min) results in a better surface roughness, Ra, for the coarse-grained sample compared to its ultrafine-grained alloy counterpart. When the cutting speed is increased by 1.5 times (up to V = 72 m/min), on the contrary, the ultrafine-grained sample has a lower surface roughness, Ra, compared to the coarse-grained sample. The differences in the morphology and microstructure of the chips, depending on the microstructure type of the processed alloy, are discussed: the presence of plastic flow lines in the chip microstructure of the turned ultrafine-grained sample and the formation of shear bands, cleavages, and microcracks in the chips of the turned coarse-grained alloy. [ABSTRACT FROM AUTHOR]

Strength and ductility synergy in ultrafine-grained AZQ310 alloy sheet was successfully improved at the expense of grain boundary segregation via multi-pass rolling. Before rolling, the as-extruded alloy has high yield strength (TYS, 382 MPa) but poor elongation (4.1%) mainly due to the ultra-fine grains (414 nm) and the co-segregation of Al/Zn atoms at grain boundaries. More importantly, this non-equilibrium segregation dies away during the rolling process, and the sheet exhibits a tensile yield strength of 370 MPa, an ultimate strength of 422 MPa, and an elongation of 9.8% along the rolling direction after 5th pass rolling. The results show that the high strength-ductility synergy is mainly attributed to the ultra-fine grains and residual dislocations. Furthermore, it is surprising that the yield point phenomenon (YPP) prominently in as-extruded sample is weakened and finally eliminated in as-rolled sheets. Microstructure evolution in the room temperature tensile test manifests that the underlying reason for the YPP is the stress-induced grain growth and grain boundary segregation, which in turn expounds the difficulty in the refining of ultrafine-grained Mg alloys by traditional processing methods.

A method is proposed for analyzing the relative energy distributions of grain boundaries in ultrafine-grained materials measured by grain boundary grooving using a scanning tunneling microscope. The grain boundary energy distribution in a grain boundary ensemble is considered as a superposition of individual distributions or populations, which can be identified by cluster analysis based on statistical criteria and each of which has its own average energy, variance, and share in the total distribution. The analysis is performed for 12Cr15Mn9NiCu steel with a coarse-grained structure in the as-received state and with an ultrafine-grained structure produced by hot helical rolling and subsequent cold rolling. It is shown that the number of boundary populations and their main characteristics revealed by clustering depend on the steel structure. The results of cluster analysis of experimental distributions are compared with the EBSD measurement data on grain boundary misorientation distributions. Discrepancy between the clustering results for the energy and misorientation distributions of grain boundaries is discussed taking into account the difference in the type of information obtained. [ABSTRACT FROM AUTHOR]

Homogeneous nanostructured and ultrafine grained (NS, UFG) states with mean grain sizes of 95 and 200 nm, respectively, have been formed in a 1565ch Al–Mg alloy (Al–5.66Mg–0.81Mn–0.67Zn–0.09Zr–0.07Cr–0.04Ti–0.001Be–0.3(Fe + Si) wt %). Microstructure of both states is represented by grain boundaries with predominantly high-angle misorientations. The alloy, produced both by high pressure torsion at room temperature and equal channel angular pressing at 200°C using the Conform approach, exhibits superplasticity at low temperatures in the range 250–300°C and strain rates in the range of 5 × 10–4–10–2 s–1. Elongation values range 170–560%, while the rate sensitivity coefficient (m) varies from 0.3 to 0.73 at low flow stress for both NS and UFG structures. The temperature range for the stability of strength properties of the 1565ch alloy in NS and UFG states after thermal and thermal mechanical treatments has been determined. The material in both structural states maintains a high level of strength after undergoing deformation under SP conditions. The deformation relief formed on the gage surface of the NS and UFG specimens of the 1565ch alloy during the established SP yield stage has been analyzed. [ABSTRACT FROM AUTHOR]

In this study, a composite with alternate layers of 5056 and 1580 alloys was manufactured with wire arc additive manufacturing technology. It is shown that increased strength characteristics of composite material can be obtained with deformation treatment using a high-pressure torsion (HPT) technique. The microstructure and mechanical properties of the HPT-processed material in different structural states were investigated. The HPT-processed material exhibits a high value of ultimate tensile strength (~770 MPa) but low ductility. Short-term annealing at 250 °C and additional deformation with HPT to 0.25 of revolution at room temperature resulted in a slight decrease in the material's strength to ~700 MPa but provided ductility of ∼9%. Physical mechanisms to improve plasticity in correlation with microstructure evolution are discussed. [ABSTRACT FROM AUTHOR]

The kinetics of microcracks accumulation and fracture at various stages of tension of grade 20 steel samples with coarse-grained and ultrafine-grained (UFG) structure obtained by equal-channel angular pressing (ECAP) has been studied. To research the effect of mechanical degradation, a part of the samples were subjected to preliminary cycling to a relative lifetime of 50%, followed by tensile tests, during which the parameters of acoustic emission and deformation fields obtained by digital image correlation were evaluated, and the intensity of the residual magnetic field was measured. The length and density of surface microcracks were measured by optical microscopy using computer image analysis. It is established that pre-cycling causes hardening of the material and a decrease in its plasticity. The fracture stages were revealed, and the origins of fatigue cracks were found on the internal delaminations of samples with a UFG structure after preliminary cyclic loading. It is shown that the formation of the UFG structure after the ECAP of samples made of grade 20 steel leads to hardening and reduction of the fracture work, the area of the plastic zone, maximum major deformations and damage, as well as to an increase in the number of AE signals and the intensity of the residual magnetic field. [ABSTRACT FROM AUTHOR]

Obtaining materials with improved and properly balanced physical and mechanical properties remains one of the main goals of materials science. At the same time, one of the most promising ways to improve the properties of metallic materials without changing and complicating their chemical and phase compositions is to obtain ultrafine-grained states within them. Such materials are characterized by high strength and high ductility. This combination of properties is crucially important for responsible products, where the weight and size of the part are important. For example, for medical implants, which, at maintaining strength, can be made thinner, and, if the load is exceeded, it will not be broken, damaging the surrounding tissues, but will only bend and can be subsequently replaced. Such a combination of strength and ductility is difficult to be obtained by other methods (e.g., heat treatment). However, for the bulk ultrafine-grained materials, in addition to the requirements for grain size, there are also requirements for the isotropism and equiaxiality of grains, the misorientation boundaries of which should be predominantly high-angle. Traditional deformation technologies (such as drawing and cold rolling) are also accompanied by structure refinement. However, in general, the substructure has a cellular character with grains elongated in the direction of drawing or rolling and contains a high proportion of low-angle boundaries. This fact contributes to the anisotropy of the properties of products in the absence of a combination of properties of high strength and ductility at the same time. Over the past 2–3 decades, the technologies of severe plastic deformation (SPD) have attracted great interest in the production of ultrafine-grained materials. However, the growth in demand is significantly limited by the high cost of manufacturing products from such materials due to the high energy and labour intensity of their production. Therefore, this article reviews and analyses contemporary technologies for the production of metals and alloys with ultrafine-grained structure, combining both high strength and ductility, by using relatively simple and inexpensive devices, which allow spending the minimum possible amount of time in the manufacture of products. The literature overview shows the level of the process to develop technology for obtaining the ultrafine-grained structure in metals and alloys. Such structures provide a combination of a high level of strength characteristics with high ductility that fundamentally distinguishes such materials from conventional ones. This is urgent for applications, where the weight, size, or special exploitation properties of the part are crucially important.

The rheological properties of the Zr-2.5Nb alloy by the strain rate range of 0.5–15 s−1 and by the temperature range of 20–770 °C was studied. The dilatometric method for phase states temperature ranges was experimentally determined. A material properties database for computer FEM simulation regards the indicated temperature-velocity ranges were created. Using this database and DEFORM-3D FEM-softpack, the radial shear rolling complex process numerical simulation was carried out. The contributed conditions for the ultrafine-grained state alloy structure refinement were determined. Based on the simulation results, a full-scale experiment of Zr-2.5Nb rod rolling a on a radial-shear rolling mill RSP-14/40 was carried out. It takes in seven passes from a diameter of 37–20 mm with a total diameter reduction ε = 85%. According to this case simulation data, the total equivalent strain in the most processed peripheral zone 27.5 mm/mm was reached. Due to the complex vortex metal flow, the equivalent strain over the section distribution was uneven with a gradient reducing towards the axial zone. This fact should have a deep effect on the structure change. Changes and structure gradient by sample section EBSD mapping with 2 mm resolution were studied. The microhardness section gradient by the HV 0.5 method was also studied. The axial and central zones of the sample by the TEM method were studied. The rod section structure has an expressed gradient from the formed equiaxed ultrafine-grained (UFG) structure on a few outer millimeters of the peripheral section to the elongated rolling texture in the center of the bar. The work shows the possibility of processing with the gradient structure obtaining and enhanced properties for the Zr-2.5Nb alloy, and a database for this alloy FEM numerical simulations are also presents. [ABSTRACT FROM AUTHOR]

The decrease of superplastic forming temperature and improvement of post-forming mechanical properties are important issues for titanium-based alloys. Ultrafine-grained and homogeneous microstructure are required to improve both processing and mechanical properties. This study focuses on the influence of 0.01–2 wt.% B (boron) on the microstructure and properties of Ti-4Al-3Mo-1V (wt.%) alloys. The microstructure evolution, superplasticity, and room temperature mechanical properties of boron-free and boron-modified alloys were investigated using light optical microscopy, scanning electron microscopy, electron backscatter diffraction, X-ray diffraction analysis, and uniaxial tensile tests. A trace addition of 0.01 to 0.1 wt.% B significantly refined prior β-grains and improved superplasticity. Alloys with minor B and B-free alloy exhibited similar superplastic elongations of 400–1000% in a temperature range of 700–875 °C and strain rate sensitivity coefficient m of 0.4–0.5. Along with this, a trace boron addition provided a stable flow and effectively reduced flow stress values, especially at low temperatures, that was explained by the acceleration of the recrystallization and globularization of the microstructure at the initial stage of superplastic deformation. Recrystallization-induced decrease in yield strength from 770 MPa to 680 MPa was observed with an increase in boron content from 0 to 0.1%. Post-forming heat treatment, including quenching and ageing, increased strength characteristics of the alloys with 0.01 and 0.1% boron by 90–140 MPa and insignificantly decreased ductility. Alloys with 1–2% B exhibited an opposite behavior. For the high-boron alloys, the refinement effect of the prior β-grains was not detected. A high fraction of borides of ~5–11% deteriorated the superplastic properties and drastically decreased ductility at room temperature. The alloy with 2% B demonstrated non-superplastic behavior and low level of strength properties; meanwhile, the alloy with 1% B exhibited superplasticity at 875 °C with elongation of ~500%, post-forming yield strength of 830 MPa, and ultimate tensile strength of 1020 MPa at room temperature. The differences between minor boron and high boron influence on the grain structure and properties were discussed and the mechanisms of the boron influence were suggested. [ABSTRACT FROM AUTHOR]

In this work, an ultrafine-grained high-Nb–TiAl alloy with a nominal composition of Ti–45Al–8Nb–0.2W–0.2B (at%) was prepared by cryomilling and subsequent spark plasma sintering (SPS) technique. The chemical composition, particle size, morphology and crystallite size of cryomilled powder were studied. It is found that cryomilling can effectively reduce the particle size and enhance grain refinement. The ingots sintered at 900 and 1000 °C show an equiaxed near-γ microstructure with grain sizes < 700 nm, while the sample sintered at 1100 °C exhibits duplex microstructure. Especially, the one sintered at 1000 °C has excellent mechanical properties, whose compression yield strength, fracture strength, bending strength and plastic strain achieve 1310, 2174, 578 MPa and 16.8%, respectively. The reasons for the effect of cryomilling and the mechanical behavior of sintered ingots were discussed. It is suggested that cryomilling in combination with SPS is an effective way to synthesize high-Nb–TiAl alloy with ultrafine-grained structure. [ABSTRACT FROM AUTHOR]

Several physics-based models have been utilized in material design for the simulation and prediction of material properties. In this study, several machine-learning (ML) approaches were used to construct a prediction model to analyze the influence of equal-channel angular pressing (ECAP) parameters on the microstructural, corrosion and mechanical behavior of the biodegradable magnesium alloy ZK30. The ML approaches employed were linear regression, the Gaussian process, and support vector regression. For the optimization of the alloy's performance, experiments were conducted on ZK30 billets using different ECAP routes, channel angles, and number of passes. The adopted ML model is an adequate predictive model which agreed with the experimental results. ECAP die angles had an insignificant effect on grain refinement, compared to the route type. ECAP via four passes of route Bc (rotating the sample 90° on its longitudinal axis after each pass in the same direction) was the most effective condition producing homogenous ultrafine grain distribution of 1.92 µm. Processing via 4-Bc and 90° die angle produced the highest hardness (97-HV) coupled with the highest tensile strength (344 MPa). The optimum corrosion rate of 0.140 mils penetration per year (mpy) and the optimum corrosion resistance of 1101 Ω·cm2 resulted from processing through 1-pass using the 120°-die. Grain refinement resulted in reducing the corrosion rates and increased corrosion resistance, which agreed with the ML findings. [ABSTRACT FROM AUTHOR]

The influence of the ultrafine-grained structure formed by equal-channel angular pressing via the "Conform" scheme on the fatigue behavior of metastable β-alloy Ti-15Mo has been studied. It is shown that the alloy with a two-phase ultrafine-grained structure achieved the best mechanical properties and enhanced fatigue endurance limit (up to 710 MPa on the basis of 107 cycles) due to the total contribution of grain boundary, dislocation, and phase strengthening mechanisms. A fractographic analysis of the fracture surface of samples after fatigue tests showed the features of fatigue crack propagation depending on the type of alloy microstructure. The general and distinctive features of fatigue failure of alloy samples in the initial coarse-grained (α + β)-, single-phase coarse-grained β-, and ultrafine-grained (α + β)-states are revealed. In all of the samples, a fatigue crack nucleated on the surface and propagated downward, i.e., perpendicular to the direction of the applied pressures. It is shown that fracture surfaces of the ultrafine-grained samples had a high roughness and were characterized by the presence of a large number of secondary cracks, as compared to the coarse-grained analogues. [ABSTRACT FROM AUTHOR]

In this work, the technique of equal-channel angular pressing (ECAP) that enables producing bulk billets was used to form a UFG structure in Ti-6Al-4V alloy. A subsequent warm upsetting simulates die forging and the production of a part. We studied the evolution of the UFG alloy’s crystallographic texture in the process of deformation during the production of a semi-product and/or a part, as well as its effect on the ductile–brittle transition region in the temperature range from −196 °C to 500 °C and the material’s fracture mechanisms. To test Charpy impact strength, standard samples of square cross-section with a V-shape notch were used (KCV). It was found that the impact toughness anisotropy is caused by textural effects and has a pronounced character at temperatures in the ductile–brittle transition range. Up to 100 °C the KCV values are close in the specimens processed by ECAP and ECAP+upsetting (along and perpendicularly to the upsetting axis—along the Z-axis and along the Y-axis, respectively), while a large difference is observed at test temperatures of 200 °C and higher. At a temperature of 500 °C, the impact toughness of the UFG Ti-6Al-4V alloy after ECAP reaches a level of that after ECAP+upsetting in the fracture direction along the Z-axis (1.60 and 1.77 MJ/m2, respectively). Additionally, an additional ECAP upsetting after ECAP decreases the ductile–brittle transition temperature of the UFG Ti-6Al-4V alloy, which increases the temperature margin of the toughness of the structural material and reduces the risk of the catastrophic failure of a product. The fractographic analysis of the fracture surface of the specimens after Charpy tests in a wide temperature range revealed the features of crack propagation depending on the type of the alloy’s microstructure and texture in the fracture direction.

In this paper, the superplastic behavior of the two-phase titanium alloy VT6 with an ultrafine-grained (UFG) structure produced by equal-channel angular pressing is examined. The deformation of specimens with a UFG structure was performed by upsetting in a temperature range of 650–750 °C and strain rate range of 1 × 10−4–5 × 10−1 s−1. Under these conditions, an increased strain-rate sensitivity coefficient m was observed. The calculation of apparent activation energy showed values in a range of 160–200 kJ/mol while the superplastic flow of the VT6 alloy was occurring. When superplastic behavior (SPB) was impeded, the energy Q grew considerably, indicating a change in mechanism from grain-boundary sliding (GBS) to bulk diffusion. A change in temperature and strain rate influenced the development of superplastic flow and the balance of relaxation processes. Microstructural analysis shows that the UFG state is preserved at upsetting temperatures of 650 and 700 °C. A decrease in strain rate and/or an increase in upsetting temperature promoted a more active development of recrystallization and grain growth, as well as α2-phase formation. In a certain temperature and strain-rate range of the UFG VT6 alloy, α2-phase plates were found, the formation of which was controlled by diffusion. The effect of the α2-phase on the alloy's mechanical behavior is discussed. [ABSTRACT FROM AUTHOR]

In this work, the strength properties and impact toughness of the ultrafine-grained (UFG) Ti-6Al-4V titanium alloy produced by severe plastic deformation (SPD) in combination with upsetting were studied, depending on the direction of crack propagation. In the billets processed by equal-channel angular pressing (ECAP), the presence of anisotropy of ultimate tensile strength (UTS) and ductility was observed, conditioned by the formation of a metallographic and crystallographic texture. At the same time, the ECAP-processed UFG alloy exhibited satisfactory values of impact toughness, ~0.42 MJ/m2. An additional upsetting of the ECAP-processed billet simulated the processes of shape forming/die forging and was accompanied by the development of recovery and recrystallization. This provided the "blurring" of texture and a reduction in the anisotropy of UTS and ductility, but a difference in impact toughness in several directions of fracture was still observed. It is shown that texture evolution during upsetting provided a significant increase in the crack propagation energy. The relationship between microstructure, texture and mechanical properties in different sections of the material under study is discussed. [ABSTRACT FROM AUTHOR]

The method of radial shear rolling makes it possible to achieve comparable to high pressure torsion (HPT) method ultrahigh degrees of total strain level in combination with the vortex metal flow character for long-length large bulk bars unable by HPT and many other processes of sever plastic deformation (SPD). Sequential rolling of the Zr-1%Nb alloy was carried out under extreme conditions on two radial shear rolling mills with a total diameter reduction ε = 185% and a maximum total strain level = 46 mm/mm. The strain level and its cross-section distribution assessment by finite element method (FEM) simulation was studied. The final bar cross-section structure type distribution detailed study 1 mm resolution by electron back scatter diffraction (EBSD) mapping was performed. A gradient structure with a predominance of the equiaxed ultrafine-grained (UFG) state was found. The deformation level rising did not allow to refine it in the periphery zone more than that obtained nearly middle of the processing, but it allows for significant change in the axial zone structure. The additional large warm deformations by radial shear rolling have no additional grain refinement effect for already 300–600 nm refined zone. An equiaxed UFG structure was obtained in a relatively large volume of the sample with a reduced gradient towards the non-UFG center zone in regard to known works. [ABSTRACT FROM AUTHOR]

This study introduces a process of severe plastic deformation (SPD) called incremental feeding high-pressure sliding (IF-HPS) where significant grain refinement is possible in an enlarged sheet area. The IF-HPS process is applied to Al alloys such as A1050, A3105, A5052 and A5182. The grain sizes were refined to the submicrometer ranges and the tensile strength increased to almost twice as much as the annealed states. The conditions for the IF-HPS process are optimized so that the tensile strength remains high without initiation of cracks. The process conditions are also investigated to achieve homogeneous development of the tensile properties throughout the processed sheets. It is demonstrated that the IF-HPS process is useful to extend the SPD-processed area without increasing the machine capacity while maintaining enhanced mechanical properties. [ABSTRACT FROM AUTHOR]

Comparative studies of the diffusion and accumulation of hydrogen in the Zr–1 wt.% Nb alloy in the finegrained and ultrafine-grained states during electrolytic saturation were carried out by the membrane method. The formation of an ultrafine-grained structure is established to lead to a decrease in the effective diffusion coefficient and the rate of hydrogen accumulation in the bulk of the alloy. The influence of the dislocation density and the length of grain boundaries on the effective diffusion coefficient of hydrogen and the ability of the alloy to accumulate hydrogen in the bulk are considered. [ABSTRACT FROM AUTHOR]

At present, researchers pay great attention to the development of metastable β-titanium alloys. A task of current importance is the enhancement of their strength and fatigue properties. An efficient method for increasing the strength of such alloys could be severe plastic deformation. The object of this study was a medical metastable β-titanium alloy Ti-15Mo (ASTM F2066). The alloy in the (α + β) state was for the first time deformed by combined processing, including equal channel angular pressing-conform and drawing. Such processing enabled the production of long-length rods with a length of 1500 mm. The aim of the work was to study the effect of the combined processing on the alloy's microstructure and mechanical properties. An ultrafine-grained structure with an average size of structural elements less than 100 nm was obtained. At the same time, high strength and ductility (σuts = 1590 MPa, δ = 10%) were achieved, which led to a record increase in the endurance limit (σ−1 = 710 MPa) under tension-compression terms. [ABSTRACT FROM AUTHOR]

This paper presents an overview of the latest trends in the development of severe plastic deformation (SPD) using rolling methods. From many scientific works, it is known that severe plastic deformation provides intense grain grinding up to ultrafine and nanosized grains during multi-cycle deformation. It is also possible to obtain a uniform or gradient grain distribution over the cross-section of the workpiece. During SPD processes, the strength parameters can be increased several times. Of all the methods considered, asymmetric rolling has become the most widespread owing to its simple implementation in production conditions. Most of the known methods and devices for asymmetric rolling are designed for deformation in rolls with a smooth barrel, while the use of rolls with a relief surface allows the processing of metal to obtain a higher level of equivalent strain. Ensuring a high asymmetry level when rolling in relief rolls allows, in addition to the development of shear strain in two transverse directions (height and width), it also provides an additional level of shear strain in the longitudinal direction. In addition to the speed asymmetry, the rolling scheme in relief rolls is also suitable for the implementation of geometric asymmetry when one of the relief rolls has a reduced or increased diameter while maintaining the relief geometry on the roll surface. [ABSTRACT FROM AUTHOR]

In this study, the microstructural behavior of the advanced Ti-5.7Al-3.8Mo-1.2Zr-1.3Sn-0.15Si (VT8M-1) alloy during rotary swaging (RS) was investigated. VT8M-1 has increased heat resistance and is considered a replacement for the Ti-6Al-4V alloy. It was shown that, during RS, the evolution of the primary a phase is characterized by the formation of predominantly low-angle boundaries according to the mechanism of continuous dynamic recrystallization. The density of low-angle boundaries increases three times: from 0.38 µm−1 to 1.21 µm−1 after RS. The process of spheroidization of the lamellar (a + b) component is incomplete. The average size of globular a and b particles was 0.3 μm (TEM). It is shown that the microstructures after RS (ε = 1.56) and equal-channel angular pressing (ECAP) (ε = 1.4) are significantly different. The temperature–velocity regime and the predominance of shear deformations during ECAP contributed to a noticeable refinement of the primary a-phase and a more complete development of globularization of the lamellar (a+b) component. EBSD studies have shown that RS leads to the formation of a structure with a higher density of low- and high-angle boundaries compared to the structure after ECAP. The results are useful for predicting alloy microstructure in the production of long rods that are further used in forging operations.

Titanium alloys are widely used in various industries. The most common and well-known titanium alloy is titanium alloy with aluminum and vanadium (Ti-6Al-4V). This alloy is used, for example, in the manufacture of aircraft engines. As part of the development of technologies and the emergence of the evolving requirements for materials, Ti-6Al-4V alloys with ultrafine grains less than 1 μm may become promising. This modification of the alloy has excellent strength characteristics, such as increased fatigue resistance. However, manufacturers are aware of the machinability problem of titanium alloys. To date, a sufficiently high level of understanding of this problem has already been achieved. But, there is practically no information about the machinability of ultrafine-grained alloys and their comparison, in this regard, with the usual coarse-grained version. This study presents the results of experimental studies on the influence of cutting parameters (cutting speed, V, m/min; feed rate, Fz, mm/rev) on the roughness and microstructure of the surface of Ti-6Al-4V samples with coarse-grained and ultrafine-grained structures produced via equal-channel angular pressing. It is shown that turning at a low cutting speed (V = 48 m/min) results in a better surface roughness, Ra, for the coarse-grained sample compared to its ultrafine-grained alloy counterpart. When the cutting speed is increased by 1.5 times (up to V = 72 m/min), on the contrary, the ultrafine-grained sample has a lower surface roughness, Ra, compared to the coarse-grained sample. The differences in the morphology and microstructure of the chips, depending on the microstructure type of the processed alloy, are discussed: the presence of plastic flow lines in the chip microstructure of the turned ultrafine-grained sample and the formation of shear bands, cleavages, and microcracks in the chips of the turned coarse-grained alloy.

The influence of severe plastic deformation and subsequent pre-recrystallization annealing on the structural-phase state and mechanical properties of the VT35 titanium alloy is studied. It is shown that the formation of an ultrafine-grained structure leads to a 65−75% increase of the room-temperature mechanical properties of this alloy compared to its initial coarse-grained state. A significant scatter in the mechanical properties of the alloy after such treatment is attributed to the inhomogeneity of the α and β phase distribution in the bulk of the workpieces. A subsequent pre-recrystallization annealing of the VT35 ultrafine-grained alloy at the temperatures of 723 and 773 K leads to an additional increase in its mechanical properties (the yield strength and ultimate tensile strength values can exceed 1700 MPa). Using the samples annealed at 723 K for 0.5 h as an example, it is shown that this increase is accounted for by a larger volume fraction of the α-phase due to the β→α phase transformation occurring inside the β phase regions and, hence, a more uniform α and β phase distribution. [ABSTRACT FROM AUTHOR]

Experimental investigations were conducted on Mg-3Zn-0.6Zr alloy under different ECAP conditions of number of passes, die angles, and processing route types, aimed at investigating the impact of the ECAP parameters on the microstructure evolution, corrosion behavior, and mechanical properties to reach optimum performance characteristics. To that end, the response surface methodology (RSM), analysis of variance, second-order regression models, genetic algorithm (GA), and a hybrid RSM-GA were utilized in the experimental study to determine the optimum ECAP processing parameters. All of the anticipated outcomes were within a very small margin of the actual experimental findings, indicating that the regression model was adequate and could be used to predict the optimization of ECAP parameters. According to the results of the experiments, route Bc is the most efficient method for refining grains. The electrochemical impedance spectroscopy results showed that the 4-passes of route Bc via the 120°-die exhibited higher corrosion resistance. Still, the potentiodynamic polarization results showed that the 4-passes of route Bc via the 90°-die demonstrated a better corrosion rate. Furthermore, the highest Vicker's microhardness, yield strength, and tensile strength were also disclosed by four passes of route Bc, whereas the best ductility at fracture was demonstrated by two passes of route C. [ABSTRACT FROM AUTHOR]

The formation of ultrafine-grained structures is a well-known method of decreasing the temperature and/or increasing the strain rate to provide superplasticity in titanium alloys. Under certain conditions, dissolved hydrogen can produce a plasticizing effect on titanium alloys, showing up as a decrease in their stress and/or an increase in their ultimate strain. Here we study the effect of 0.3 wt % of dissolved hydrogen on the structure, phase state, and superplastic properties of an ultrafine-grained (α + β) Ti-Al-V-Mo system (VT16 alloy) at a temperature of 823–923 K. The ultrafine-grained structure of Ti-Al-V-Mo (VT16 alloy) and Ti-Al-V-Mo-0.3 wt % H (VT16-H alloy) results from severe plastic deformation via uniaxial compression with a change in the strain axis and in the temperature from 1023 to 823 K. In the temperature range used, the presence of hydrogen in the solid solution of VT16 alloy decreases its superplastic properties. During deformation, hydrogen is redistributed in the bulk of the material by elastic stress fields and is accumulated in the most stressed regions, leading to plastic strain localization and to a decrease in the strain to fracture. The release of hydrogen from VT16-H alloy during deformation activates its β → α transformation and associated diffusion redistribution of its alloying elements, contributing to the accommodation of grain boundary sliding and to the increase in the strain to fracture. [ABSTRACT FROM AUTHOR]

The effect of two regimes of all-round isothermal forging (AIF) in a hydraulic press and subsequent annealing on the structure and mechanical properties of structural low-carbon steel 12GBA is analyzed. Steel structure is studied by the EBSD method and scanning electron microscopy. Steel mechanical properties are determined in tensile tests. Total impact energy in the loading diagrams is plotted in terms of the energy expended on crack generation and propagation. It is shown that AIS forms a relatively equiaxed ultrafine-grained (UFG) structure. Formation of an equiaxed UFG structure with grain/subgrain sizes of 0.4 – 0.5 μm during forging doubles strength properties and retains ductility at a good enough level compared with the initial fine-grained structure. The ductile-brittle transition temperature is lowered. UFG steel has a better impact strength below –40°C compared with the initial condition. Additional annealing at 550°C increases impact strength and shifts the ductile-brittle transition temperature towards lower values. [ABSTRACT FROM AUTHOR]

In this study, billets of the ZK30 (Mg-3Zn-0.6 Zr-0.4 Mn, wt%) alloy were Equal Channel Angle Pressing (ECAP) processed for up to four passes of routes Bc (with rotating the sample 90° in the same direction between the subsequent passes), A (without sample rotation), and C (with sample rotating 180°) after each pass at a temperature of 250 °C and a ram speed of 10 mm/min using a die with an internal channel angle of 90°. The microstructural evolution and the crystallographic texture were investigated using a Scanning Electron Microscope (SEM) equipped with the Electron Back-Scatter Diffraction (EBSD) technique. Corrosion measurements were conducted in ringer lactate which is a simulated body fluid. The Vickers microhardness test and tensile tests were conducted for the alloy before and after processing. The as-annealed billets exhibited a bimodal structure as fine grains (more than 3.39 µm) coexisted with almost-equiaxed coarse grains (less than 76.73 µm); the average grain size was 26.69 µm. Further processing until four passes resulted in enhanced grain refinement and full Dynamic Recrystallization (DRX). ECAP processing through 4-Bc, 4-A, and 4-C exhibited significant reductions in grain size until they reached 1.94 µm, 2.89 µm, and 2.25 µm, respectively. Four-pass processing also resulted in the transformation of low-angle grain boundaries into high-angle grain boundaries. The previous conclusion was drawn from observing the simultaneous decrease in the fraction of low-angle grain boundaries and an increase in the fraction of high-angle grain boundaries. The pole figures revealed that 4-Bc, 4-A, and 4-C reduced the maximum texture intensity of the as-annealed billets. The potentiodynamic polarization findings revealed that route Bc is the most effective route in improving the corrosion rate, whereas the Electrochemical Impedance Spectroscopy (EIS) revealed that routes A and Bc improved the corrosion resistance with nearly identical values. Finally, 4-Bc resulted in the highest increase in Vickers hardness, yield stress, and ultimate tensile strength with values of 80.8%, 19.3%, and 44.5%, alongside a 31% improvement in ductility, all compared to the AA condition. [ABSTRACT FROM AUTHOR]

In this study, a composite with alternate layers of 5056 and 1580 alloys was manufactured with wire arc additive manufacturing technology. It is shown that increased strength characteristics of composite material can be obtained with deformation treatment using a high-pressure torsion (HPT) technique. The microstructure and mechanical properties of the HPT-processed material in different structural states were investigated. The HPT-processed material exhibits a high value of ultimate tensile strength (~770 MPa) but low ductility. Short-term annealing at 250 °C and additional deformation with HPT to 0.25 of revolution at room temperature resulted in a slight decrease in the material’s strength to ~700 MPa but provided ductility of ∼9%. Physical mechanisms to improve plasticity in correlation with microstructure evolution are discussed.

Magnesium-Zinc-Zirconium (Mg-Zn-Zr) alloys have caught considerable attention in medical applications where biodegradability is critical. The combination of their good biocompatibility, improved strength, and low cytotoxicity makes them great candidates for medical implants. This research investigation is focused on providing further insight into the effects of equal channel angular processing (ECAP) on the corrosion behavior, microstructure evolution, and mechanical properties of a biodegradable ZK30 alloy. Billets of Mg-3Zn-0.6 Zr (ZK30) alloy were processed through ECAP up to 4 passes of route Bc (rotating the billets 90° in the same direction between the subsequent passes) at 250 °C. Electron back-scatter diffraction (EBSD) was utilized to investigate the microstructural evolution as well as the crystallographic texture. Several electrochemical measurements were carried out on both a simulated body fluid and a 3.5% sodium chloride (NaCl) solution. Mechanical properties such as Vicker's hardness and tensile properties were also assessed. The as-annealed (AA) microstructure was dominated by equiaxed coarse recrystallized grains with an average grain size of 26.69 µm. After processing, a geometric grain subdivision took place due to the severe plastic deformation. Processed samples were characterized by grain refinement and high density of substructures. The 4-passes sample experienced a reduction in the grain size by 92.8% compared with its AA counterpart. The fraction of high-angle grain boundaries increased significantly after 4-passes compared to the 1-pass processed sample. With regards to the crystallographic texture, the AA condition had its {0001} basal planes mostly oriented parallel to the transversal direction. On the other hand, ECAP processing resulted in crystallographic texture changes, such as the shifting of the ZK30 shear plane to be aligned at 45° relative to the extrusion direction (ED). Furthermore, the maximum texture intensity was reduced from 14 times random (AA billets) to 8 times random after ECAP processing through 4-passes. The corrosion rate of the 4-passes sample was tremendously reduced by 99% and 45.25% compared with its AA counterpart in the simulated body fluid and the NaCl solution, respectively. The pitting corrosion resistance of ZK30 showed notable improvements in the simulated body fluid by 471.66% and 352% during processing through 1-pass and 4-passes, respectively, compared with the 3.5% NaCl findings. Finally, significant improvements in the tensile strength, hardness, and ductility were also achieved. [ABSTRACT FROM AUTHOR]

Grain reduction in a widely used Ti-6Al-4V alloy increases its endurance limit at room temperature. In this work, the behavior of the ultrafine-grained alloy under cyclic load at the temperature of 625 K is considered. Research was conducted to examine the fatigue life in a low-cycle area of the ultrafine-grained Ti-6Al-4V alloy produced by equal-channel angular pressing. Tensile and fatigue testing of the Ti-6Al-4V samples with coarse-grained (CG) and ultrafine-grained (UFG) structures were carried out at 293 and 625 K. The alloy demonstrated an enhanced strength and fatigue life at both temperatures. The representative features of the microstructural evolution and the fracture features in the UFG and CG alloys after fatigue tests are described in detail. The prospects for the use of the UFG Ti-6Al-4V alloy for engineering applications, such as in the production of critical gas-turbine engine parts, is discussed. [ABSTRACT FROM AUTHOR]

Here, the two‐phase titanium alloy Ti‐5.7Al‐3.8Mo‐1.2Zr‐1.3Sn (Russian name VT8M‐1) with an ultrafine‐grained (UFG) structure is successfully produced by equal‐channel angular pressing (ECAP). This UFG alloy demonstrates a significant increase in strength at room temperature (RT) and superplastic‐like behavior during compression at elevated temperatures in a range of 650–800 °C. This unusual behavior is used in this work to study the forging of the alloy at 700 °C, which simulates the process of making an aircraft engine blade. It is shown that after this forging the alloy has significantly higher strength properties than after standard processing. The origin of such superior behavior of this UFG alloy is discussed. [ABSTRACT FROM AUTHOR]

Abstract—The effect of preliminary thermal cycling and annealing performed in the range of aging temperatures on the microstructure and mechanical behavior of a TiNi alloy is considered. The structure in the initial state consists of almost dislocation-free austenite grains. Equal-channel angular pressing results in an ultra-fine grained (UFG) structure consisting of equiaxed grains with an average size of 400 nm in the Ti49Ni51 alloy. The maximum number of thermal cycles is n = 100. The yield strength decreases when the number of thermal cycles increases to n = 100, which can be attributed to a saturation effect. The significant decrease in the yield strength at n = 100 can be associated with a high density of defects and aging particles, which cause the fracture of samples at lower tensile strength values, making dislocation motion difficult. Thermal cycling and subsequent annealing at 400°C do not change the grain size. The results of tensile tests show that thermal cycling (n = 100) and subsequent aging increase the tensile strength and yield strength in the UFG state. [ABSTRACT FROM AUTHOR]

In this paper, the effect of hydrogenation, in the amount of 0.15 wt.%, on the short-term creep of a titanium Ti-2.9Al-4.5V-4.8Mo alloy in fine-grained (FG) and ultrafine-grained (UFG) states is studied at 723 K. The UFG structure was formed by the method of pressing with the change of the deformation axis and gradual temperature decrease. Creep tests are performed under conditions of uniaxial tension at a constant load for the creep rates at an interval of (10−7 ÷ 10−6) s−1. The UFG alloy's resistance to creep under the investigated conditions is revealed to be substantially lower than in the FG state. When hydrogen presents in the alloy in a solid solution, a 1.3–2.5-fold rise in the value of the steady-state creep rate for the hydrogenated FG and UFG alloys is observed. The creep of the non-hydrogenated FG and UFG alloys is described by the creep power law. The presence of dissolved hydrogen leads to a violation of the creep power law. The values of stress sensitivity indices, steady-state creep rate, and effective creep activation energy are determined. The relationships between the hydrogenation, structure, and creep mechanisms of the alloy at the steady-state are discussed. [ABSTRACT FROM AUTHOR]

This work is devoted to the study of the possibility of recycling bar scrap of stainless metals using radial-shear rolling. In the course of studies on the deformation of bar scrap in the form of pins made of 12X18N9T stainless austenitic steel on a radial-shear rolling mill, the resulting bar was obtained microstructure of two different types: on the periphery an equiaxed ultrafine-grained structure with a grain size of 0.4–0.6 microns was formed; in the axial zone anoriented, banded texture was obtained. This discrepancy in the structure of the peripheral and axial zones, together with the results of cross-section microhardness measurements of samples made of 12X18N9T austenitic stainless steel with a total degree of deformation of 44.4 %, indicates the gradient nature of the resulting microstructure.

[Display omitted] • NS state Al-Zn-Mg-Cu alloy provides superductility at 170 °C. • Under LTSP conditions in NS Al-Zn-Mg-Cu alloy the GBS is realized. • LTSP does not cause degradation of the grain structure and properties. • NS Al-Zn-Mg-Cu alloy demonstrates formability at 170 °C. The evolution of Al-Zn-Mg-Cu alloy microstructure during high pressure torsion at room temperature and subsequent low-temperature superplastic deformation is studied. The formation of a nanostructured state in Al-Zn-Mg-Cu alloy made it possible to implement a superplasticity (SP) effect at 170 °C and a strain rate of 5 × 10−4 s−1. The deformation relief of the gauge part of an Al-Zn-Mg-Cu alloy sample at the stage of steady-state SP flow is analyzed. Low-temperature superplastic deformation is stated to take place due to grain boundary sliding. High formability of nanostructured alloy under biaxial tension at a temperature of 170 °C is recorded. [ABSTRACT FROM AUTHOR]

The decrease of superplastic forming temperature and improvement of post-forming mechanical properties are important issues for titanium-based alloys. Ultrafine-grained and homogeneous microstructure are required to improve both processing and mechanical properties. This study focuses on the influence of 0.01–2 wt.% B (boron) on the microstructure and properties of Ti-4Al-3Mo-1V (wt.%) alloys. The microstructure evolution, superplasticity, and room temperature mechanical properties of boron-free and boron-modified alloys were investigated using light optical microscopy, scanning electron microscopy, electron backscatter diffraction, X-ray diffraction analysis, and uniaxial tensile tests. A trace addition of 0.01 to 0.1 wt.% B significantly refined prior β-grains and improved superplasticity. Alloys with minor B and B-free alloy exhibited similar superplastic elongations of 400–1000% in a temperature range of 700–875 °C and strain rate sensitivity coefficient m of 0.4–0.5. Along with this, a trace boron addition provided a stable flow and effectively reduced flow stress values, especially at low temperatures, that was explained by the acceleration of the recrystallization and globularization of the microstructure at the initial stage of superplastic deformation. Recrystallization-induced decrease in yield strength from 770 MPa to 680 MPa was observed with an increase in boron content from 0 to 0.1%. Post-forming heat treatment, including quenching and ageing, increased strength characteristics of the alloys with 0.01 and 0.1% boron by 90–140 MPa and insignificantly decreased ductility. Alloys with 1–2% B exhibited an opposite behavior. For the high-boron alloys, the refinement effect of the prior β-grains was not detected. A high fraction of borides of ~5–11% deteriorated the superplastic properties and drastically decreased ductility at room temperature. The alloy with 2% B demonstrated non-superplastic behavior and low level of strength properties; meanwhile, the alloy with 1% B exhibited superplasticity at 875 °C with elongation of ~500%, post-forming yield strength of 830 MPa, and ultimate tensile strength of 1020 MPa at room temperature. The differences between minor boron and high boron influence on the grain structure and properties were discussed and the mechanisms of the boron influence were suggested.